Nano-hybrid ORMOCER for the bulk-fill technique in the posterior region

The range of products available in the field of direct composites has expanded greatly in recent years.[1–3] In addition to the classic universal composites, the enormous rise in patients’ aesthetic expectations has resulted in the launch of a large number of so-called “aesthetic composites” on the market, which are characterised by composite materials in a sufficient number of different shades and different grades of translucency and opacity.[4] Opaque dentine shades, translucent enamel pastes and, if required, body shades make it possible to achieve highly aesthetic direct restorations using the multicoloured layering technique. They are practically indistinguishable from the dental hard tissue, and they rival the aesthetics of all-ceramic restorations. Some of these composite systems consist of more than 30 different composite materials of various shades and degrees of translucency. It is, however, essential to have appropriate experience in the handling of these materials, which are primarily used in the anterior region with a layering technique employing two or three different opacities and translucencies.[4,5]

Owing to their polymerisation properties and limited depth of cure, light-curing composites are generally used in a layering technique with individual increments of no more than 2 mm in thickness. Each increment is polymerised separately, with exposure times ranging from 10 to 40 seconds, depending on the power of the curing light and colour or translucency of the composite paste.[6] With the materials available up until recently, thicker composite layers resulted in insufficient polymerisation of the composite resin and thus in poorer mechanical and biological properties.[7–9] Applying the composite in 2 mm increments can be a very time-consuming procedure, especially in large posterior cavities. Consequently, there is considerable demand in the market for composite-based materials that are simple and quick to use, and therefore more economical, for this range of indications.[10] In order to satisfy this demand, bulk-fill composites have been developed over recent years that, given a sufficiently powerful curing light, can be placed more quickly in the cavity, using a simplified application technique, in layers 4–5 mm thick and with short increment curing times of 10–20 seconds.[11, 12, 6, 13, 14]

Taken literally, “bulk fill” means that they can be used to fill the cavity in a single step lege artis without the need for a layering technique.[15] With plastic restorative materials, this is currently only possible with cements and chemically activated or dual-curing core build-up composites. However, the former do not possess adequate mechanical properties for restorations that are clinically stable in the long term in the masticatory load-bearing posterior region of the permanent dentition and are consequently only suitable for use as interim restorations or long-term temporaries.[16-18] The latter are neither approved as restoratives nor suitable for such indications from a handling perspective (e.g. shaping of occlusal surfaces). The bulk-fill composites currently available for the simplified filling technique in the posterior region are not actually bulk materials in the true sense when examined more precisely, as the approximal extensions of clinical cavities, in particular, are generally deeper than the maximum depth of cure (4–5 mm) specified for these materials.[19,20] That said, it is possible to fill cavities with depths of up to 8 mm in two increments if a suitable material is selected—and this covers the majority of defect dimensions encountered in routine clinical practice.

Most composites contain organic monomer matrices based on conventional methacrylate chemistry.[21] Silorane technology[22–27] and ORMOCER chemistry[23–35] present alternative approaches. ORMOCERs (organically modified ceramics) are organically modified, non-metallic inorganic composites.[36] Ormocers can be classified between inorganic and organic polymers and possess both an inorganic and an organic network.[37,38,34] This group of materials was developed by the Fraunhofer Institute for Silicate Research in Würzburg in Germany and marketed for the first time as a dental restorative material in 1998 in collaboration with partners in the dental industry.[33,34] Since then, there has been considerable further development of ORMOCER-based composites for this range of application. However, the use of ORMOCERs is not limited to dental restoratives. These materials have been successfully employed for years in fields such as electronics, microsystems technology, plastic refining, preservation, anticorrosion coatings, functional coatings for glass surfaces, and highly resistant, scratch-proof protective coatings.[39–41]

ORMOCER-based dental restorative composites are currently available from two dental companies, VOCO (Admira product range) and DENTSPLY (Ceram·X). In the dental ORMOCER products to date, additional methacrylates were added to the pure ORMOCER chemistry (as well as initiators, stabilisers, pigments and inorganic fillers) in order to improve workability.[41] Therefore, it is more accurate to refer to ORMOCER-based composites.

According to the manufacturer, the new bulk-fill ORMOCER Admira Fusion x-tra (VOCO), launched in 2015, no longer contains any conventional monomers in addition to the ORMOCERs in the matrix. It features a nano-hybrid filler technology with an inorganic filler content of 84% by weight. It is available in a universal shade and displays polymerisation shrinkage of just 1.2% by volume and consequently low shrinkage stress. Admira Fusion x-tra can be applied in layers of up to 4 mm, with each increment being cured in 20 seconds (curing light intensity of > 800 mW/cm²). The malleable consistency and the other material properties of Admira Fusion x-tra allow the dentist to restore cavities using the bulk technique with a single material; an occlusal covering layer with an additional composite—as required when flowable bulk composites are used—is no longer necessary.

Clinical case
A 47-year-old patient presented at our clinic requesting the gradual replacement of his remaining amalgam fillings with tooth-coloured restorations. In the first treatment session, we replaced the old amalgam filling in tooth #46 (Fig. 1). The tooth was immediately responsive to the cold test and the percussion test too was normal. Having been informed of the possible treatment alternatives and their costs, the patient elected to have a composite restoration with Admira Fusion x-tra using the bulk-fill technique.

Treatment started with thorough cleaning of the tooth with a fluoride-free prophylaxis paste and a rubber cup to remove external deposits. As Admira Fusion x-tra is only available in a universal shade, there is no need for detailed determination of the tooth shade. After administration of local anaesthetic, the amalgam was carefully removed from the tooth (Fig. 2). After excavation, the cavity was finished with a fine-grit diamond bur and a rubber dam was placed to isolate the tooth (Fig. 3). The rubber dam separates the operating site from the oral cavity, facilitates clean and effective working, and guarantees that the working area remains free of contaminating substances, such as blood, sulcular fluid and saliva. Contamination of the enamel and dentine would result in considerably poorer adhesion of the composite to the dental hard tissue and would endanger the optimal marginal integrity of the restoration for long-term success. Additionally, the rubber dam protects the patient from irritating substances, such as the adhesive product. The rubber dam is thus an essential aid in ensuring quality and facilitating work in the adhesive technique. The minimal effort required in applying the rubber dam is compensated for by avoiding the changing of cotton rolls and the patient’s requests for rinsing.

The cavity was then demarcated with a sectional matrix made of metal (Fig. 4). The universal adhesive Futurabond M+ (VOCO) was chosen for the adhesive pretreatment of the dental hard tissue. Futurabond M+ is a modern one-bottle adhesive compatible with all conditioning techniques: the self-etch technique and the phosphoric acid-based conditioning techniques (selective enamel etching or complete etch-and-rinse pretreatment of enamel and dentine). In this case, we chose the selective enamel etching technique, applying 35% phosphoric acid (Vococid, VOCO) along the enamel margins and allowing it to work for 30 seconds (Fig. 5). The acid was then rinsed off for 20 seconds with a compressed air and water jet, and excess water carefully removed from the cavity with compressed air (Fig. 6).

Figure 7 shows the application of a generous amount of Futurabond M+ to the enamel and dentine with a micro-brush. The adhesive was thoroughly rubbed into the dental hard tissue with the applicator for 20 seconds. The solvent was then carefully evaporated with dry, oil-free compressed air (Fig. 8) and the bonding agent light cured for 10 seconds (Fig. 9). The result was a shiny cavity surface, evenly covered with adhesive (Fig. 10). This should be carefully checked, as any areas of the cavity that appear matt are an indication that insufficient adhesive was applied to those sites. In the worst case, this could result in both reduced bonding of the restoration in these areas and reduced dentine sealing, which may lead to postoperative sensitivity. If such areas are found in the visual inspection, additional bonding agent must again be selectively applied to them.

In the next step, the cavity, measured in advance with a periodontal probe (6 mm deep from the floor of the box to the occlusal marginal ridge), was filled with Admira Fusion x-tra in the area of the mesial box until a residual depth in the entire cavity of no more than 4 mm remained. At the same time, the mesial approximal surface was built up completely to the level of the marginal ridge (Fig. 11). The restorative material was cured by a polymerisation lamp (light intensity of > 800 mW/cm²) for 20 seconds (Fig. 12). The build-up of the mesial approximal surface converted the original Class II cavity into an effective Class I cavity, and then the matrix system was removed, as it was no longer required (Fig. 13). This facilitated access to the cavity with hand instruments for shaping the occlusal structures in the further course of the treatment and, owing to the improved visibility of the treatment area, allowed improved visual control of the material layers subsequently applied. The second increment of Admira Fusion x-tra filled the residual volume of the cavity completely (Fig. 14). After the shaping (Fig. 15) of a functional, but uncomplicated, occlusal anatomy—which also helps to ensure rapid finishing and polishing—the restorative material was cured again for 20 seconds (Fig. 16). The vestibular cavity was filled in the next step.

After removal of the rubber dam, the restoration was carefully finished with rotary instruments and abrasive discs, and the static and dynamic occlusion adjusted. Diamond-impregnated silicone polishers (Dimanto, VOCO) were then used to give the surface of the restoration a smooth and shiny finish. Figure 17 shows the finished direct ORMOCER restoration, which reproduced the original tooth shape with an anatomically functional occlusal surface, physiologically shaped approximal contact and aesthetically acceptable appearance. Finally, a foam pellet was used to apply the fluoride varnish (Bifluorid 12, VOCO) to the teeth.

Final remarks
The importance of direct composite-based restorative materials will continue to increase in the future. They produce scientifically verified, high-quality permanent restorations for the masticatory load-bearing posterior region, and the reliability of these has been documented in the literature. The results of an extensive review have shown that the annual loss rate for composite restorations in the posterior region (2.2%) is not statistically different from that of amalgam restorations (3.0%).[43]

The increasing economic pressure in the health care sector has created the need for a simpler, faster and thus more cost-effective basic treatment alongside the time-consuming high-end restorations. For some time now, there have been composites with optimised depths of cure on the market for this purpose that can be used to create clinically and aesthetically acceptable posterior restorations using a procedure that is more cost-effective compared with traditional hybrid composites.[44,45] In addition to the bulk-fill composites with classic methacrylate chemistry, the range of products on offer in the field of composite adhesive materials with a large depth of cure has now been expanded with a nano-hybrid ORMOCER version.

Editorial note: A list of references is available from the publisher. The article was published in Dental Tribune Nordic Vol.1, No.3.